Group therapy is the most popular form of treatment for AOD problems and there are many reports of its beneficial effects. Yet some research has reported negative effects. Specifically, studies have found that aggregating youth with conduct disorder (CD) created environments in which youth exhibited negative behavior that was positively reinforced by other group members (i.e., "deviancy training"). Other studies have suggested that antisocial behavior and deviancy training also were affected by group leader behaviors. These findings suggest that while (a) CD group composition, (b) member-reinforced disruptive behavior in groups, and (c) leadership behavior may have independent effects on outcomes, they likely interact to produce diverse outcomes. This exploratory/developmental study (R-21) will examine the influence of CD group composition (i.e., proportion of CD among group members), disruptive behavior in group (i.e., antisocial behavior and deviancy training), and group leader behaviors (i.e., negative and positive) on changes in AOD use over t me. This study tests whether the interactions of group leader behaviors with group disruptive behavior mediate changes in the trajectory of AOD behaviors over sessions and through follow-up. Data derive from a recently completed NIAAA clinical trial that involved 122 youths randomly assigned to 21 groups using the Westchester Model Student Assistance Program protocol. In the proposed study, trained evaluators will review audio tapes and transcripts of each group session to assess group leader behaviors and disruptive behavior. This research is important because: (1) it will identify the factors that contribute to iatrogenic effects to help inform the development of effective group treatment approaches; (2) it incorporates the best representation of factors thought to contribute to iatrogenic effects, and applies them to AOD group treatment; (3) it incorporates statistical methods to understand the independent, combined, and longitudinal influences of composition, disruptive behavior, and leader behaviors, on outcomes; and (4) it will make recommendations about the compositional mix of treatment groups of youths with CD, and what leader behaviors reduce disruptive group behavior. We believe this research is innovative and significant in its approach to understanding factors influencing group treatment effectiveness, and ultimately will improve clinical approaches to adolescents with AOD problems.